This invention relates to detergent formulations built with zeolites and also containing alkali silicates. More particularly, it relates to particulate detergent compositions wherein the zeolite agglomerates are more readily dispersible in the wash water. Specifically, the dispersibility of the zeolite agglomerates is improved by including an anionic functional organosiliconate and a complexing agent for trivalent aluminum in the detergent composition.
Alkali silicates have been widely used in laundry detergents for many years. In addition to providing alkalinity and buffering, alkali silicates are important as corrosion inhibitors and process aids that improve the bead strength of detergent powders. Recent developments such as the reduction in the amount of phosphates in detergents; increased use of surfactants with unique properties; and the higher cost of energy, which affects household washing temperatures as well as the cost of manufacturing detergents by spray drying have compelled many changes in detergent formulations.
However, because of the nature of detergents as complex mixtures of ingredients, changing one component or process method can generate several new problems. In particular, the use of zeolites in detergents to replace all or part of the phosphates in formulations also containing alkali silicates has produced agglomerates that deposit on the fabric being laundered and are especially noticeable as white particulate material on dark fabrics. It has been suggested that the zeolite agglomeration results from the interaction of the zeolite with other detergent ingredients during the spray drying process.
Alkali silicates have been implicated as a component of detergents that may interact with zeolites to bind particles together and form nondispersible agglomerates. Consequently, it has been proposed that only limited amounts of silicate, 3% or less, should be used in zeolite built laundry detergents. Moreover, larger amounts of alkali silicates have been reported to decrease the ion exchange capacity and the rate of ion exchange of the zeolites in a formulated detergent. However, reducing the amount or eliminating alkali silicates in detergent formulations is not a satisfactory solution because it results in the loss or reduction of the valuable properties such as bead formation and anticorrosion that the silicate provides.
Considerable effort has been expended in attempts to develop commercially viable ways of making alkali silicates and zeolites compatible in detergent formulations. For example, U.S. Pat. No. 4,157,978 teaches that multimeric silicates can be "capped" by aluminum diacetate groups and incorporated in spray dried detergent compositions to provide an overall improvement in the physical characteristics and rate of solubility of the resulting detergent granules. The patent also suggests that other "capped" silicate materials known in the art can be used in detergent formulations. As an example of such other "capped" silicates, the patent describes silicates "capped" by triorganosilyl groups.
U.S. Pat. Nos. 4,138,363, 4,216,125, 4,243,545, and 4,534,880 teach that the tendency of zeolites to agglomerate during detergent processing can be reduced by treating the zeolite surface with a hydrophilic functional silane or an anionic functional organosiliconate. Taking a somewhat different approach, U.S. Pat. No. 4,549,979 teaches that by combining an anionic functional organosiliconate with the silicate in detergent compositions containing zeolite, the solubility characteristics of the silicate are modified so that the zeolite agglomerates more readily breakup and disperse in the wash water. Particulate detergents containing the anionic functional organosiliconate according to U.S. Pat. No. 4,549,979 dispersed well in water when first made, but after periods of shelf aging, the dissolution characteristics of the zeolite agglomerates deteriorated dramatically.